# std::swap(std::basic_string)

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< cpp‎ | string‎ | basic string

Defined in header `<string>` |  |
template< class CharT, class Traits, class Alloc > void swap( std::basic_string<CharT, Traits, Alloc>& lhs, std::basic_string<CharT, Traits, Alloc>& rhs ); |  | (until C++17)
template< class CharT, class Traits, class Alloc > void swap( std::basic_string<CharT, Traits, Alloc>& lhs, std::basic_string<CharT, Traits, Alloc>& rhs ) noexcept(/* see below */); |  | (since C++17) (constexpr since C++20)

Specializes the std::swap algorithm for std::basic_string. Swaps the contents of lhs and rhs.

Equivalent to lhs.swap(rhs).

### Parameters

lhs, rhs | - | strings whose contents to swap

### Return value

(none)

### Complexity

Constant.

### Exceptions `noexcept` specification: noexcept(noexcept(lhs.swap(rhs))) | (since C++17)

### Example

Run this code

    #include <iostream>
    #include <string>

    int main()
    {
        std::string a = "AAA";
        std::string b = "BBBB";

        std::cout << "Before swap:\n"
                     "a = " << a << "\n"
                     "b = " << b << "\n\n";

        std::swap(a, b);

        std::cout << "After swap:\n"
                     "a = " << a << "\n"
                     "b = " << b << '\n';
    }

Output:

    Before swap:
    a = AAA
    b = BBBB

    After swap:
    a = BBBB
    b = AAA

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 2064 | C++11 | non-member `swap` was noexcept and inconsistent with member `swap` | noexcept removed

### See also

swap | swaps the contents (public member function)

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